CVE-2026-1999 in GitHub
Summary
by MITRE • 02/18/2026
A Server-Side Request Forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an authenticated user to access internal services bound to loopback or unspecified addresses, potentially disrupting background job processing, accessing administrative endpoints, metrics, and profiling data, or manipulating job queues. Exploitation required an authenticated user with permissions to configure webhooks (repository, organization, or GitHub App administrator privileges). This vulnerability affected all versions of GitHub Enterprise Server prior to 3.20 and was fixed in versions 3.14.22, 3.15.17, 3.16.13, 3.17.10, 3.18.4, and 3.19.1. This vulnerability was reported via the GitHub Bug Bounty program.
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Analysis
by VulDB Data Team • 03/03/2026
This Server-Side Request Forgery vulnerability in GitHub Enterprise Server represents a critical access control flaw that enables authenticated attackers to bypass network segmentation and access internal system resources. The vulnerability stems from insufficient validation of user-supplied URLs in webhook configuration functionality, allowing malicious actors to craft requests that target loopback addresses or unspecified network interfaces. Such flaws typically fall under CWE-918, which specifically addresses server-side request forgery vulnerabilities where applications fail to properly validate and sanitize external input before making requests to internal services.
The technical implementation of this vulnerability exploits the trust relationship between the GitHub Enterprise Server and its internal network components. When users configure webhooks, the system processes the provided URLs without adequate sanitization of protocol handlers or address specifications. This allows an attacker to specify URLs that resolve to localhost, 127.0.0.1, or other internal network addresses, effectively enabling them to probe and interact with services running on the same host. The impact extends beyond simple information disclosure to include potential service disruption and administrative access, as the attacker can target background job processors, metrics endpoints, and profiling systems that are typically protected by network segmentation.
From an operational perspective, this vulnerability creates significant risk for organizations relying on GitHub Enterprise Server for code management and CI/CD pipelines. The requirement for webhook configuration privileges means that the attack vector is limited to users with repository, organization, or GitHub App administrator rights, but these roles are often granted to trusted team members and administrators. The exploitation could lead to unauthorized access to job queue manipulation, which might allow attackers to disrupt continuous integration processes, access sensitive build artifacts, or even gain deeper system access through manipulation of background processes. This aligns with ATT&CK technique T1078.004, which covers valid accounts used for lateral movement, as the vulnerability leverages legitimate administrative privileges to access internal systems.
The remediation approach requires immediate deployment of patched versions across all affected GitHub Enterprise Server installations, with particular attention to version 3.14.22, 3.15.17, 3.16.13, 3.17.10, 3.18.4, and 3.19.1. Organizations should also implement network segmentation controls to limit access to internal services, particularly those running on loopback interfaces. Additional mitigations include implementing strict URL validation for webhook configurations, monitoring for suspicious webhook activity, and conducting regular security assessments of internal service exposure. The vulnerability's classification under CWE-918 underscores the importance of implementing proper input validation and network boundary controls to prevent similar issues in other applications. Security teams should also consider implementing automated monitoring for internal service access patterns that could indicate exploitation attempts, as the vulnerability's impact extends to system stability and data integrity through job queue manipulation.